1. Field of the Invention
The invention relates to a tubular cored electrode for producing a fusion-welded connection of parts of high-strength steels with a minimum yield point (RP0.2) of the weld metal of 690 N/mm2, comprising a metal tube with an outer diameter of less than 2 mm, which surrounds a filler flux core and optionally bears a coating.
Furthermore, the invention relates to a method for the essentially continuous production of tubular cored electrodes with a diameter of less than 2 mm, for the production of a fusion-welded connection of parts of high-strength steels with a minimum yield point (RP0.2) of the weld metal of 690 N/mm2 essentially with a production sequence: provision of a metal strip, forming of the metal strip in the longitudinal direction to form an essentially U-shape in cross section, insertion of filler flux into the U-shaped strip, reshaping the strip to form a tube with a joint of lateral faces bearing against one another and a filler wire flux core, connection of the joint by welding, deformation of the cross section and optionally coating of the surface of the tube or of the electrode.
2. Discussion of Background Information
Tubular cored electrodes are used for connecting parts by fusion welding as a welding filler material. In a welding device, the electrode wire is removed from a stock, for example a wire reel, and the wire is discharged from a feed or conveyor, to a so-called welding head, for an arc fusion welding, in which the electric energy supply to the electrode also takes place.
The welding head can be hand-guided or moved mechanically, whereby an automatic welding can optionally take place up to the use of computer-controlled welding robots.
A tubular cored electrode is a tubular electrode and contains inside chiefly mineral constituents and/or deoxidants and/or metallic constituents, in particular for alloying the welding melt. The composition of the filler flux core is carefully selected and the constituents should thereby be present in a form that at least does not negatively affect the welding process as well as guaranteeing a high weld seam quality.
For a supply of the welding energy to the tubular cored electrode, a bare metal surface of the same is necessary. The electrode surface is frequently copper-plated for better conducting of the current, which in addition results in a prevention of oxidation.
To avoid the formation of pores and/or cracks in the weld metal, it is important to keep the moisture content as low as possible, particularly in the filler powder of the electrode, so that a hydrogen absorption by the molten welding filler material is largely avoided during the arc welding.
In order to avoid an absorption of moisture by the filler flux during the storage of the electrode, essentially two production variants are available according to the prior art.
With one method of production of a tubular cored electrode, filler flux is inserted as homogenously as possible into a tight tube, the tube end sides are closed and the primary material thus provided is rolled to form wire and/or subjected to a tensile strain. A high strain-hardening of the tube wall in the course of the deformation can be overcome by annealing treatments of the intermediate product.
A further known production method for tubular cored electrode primary material lies in shaping a metal strip to form a U-shaped cross-sectional form, filling the U-shape with filler flux with subsequent reshaping to form a tube and an inductive welding of the axial joint surfaces. A primary material of this type with an outside diameter of 30 mm, for example, as mentioned above, can be further shaped to form a filler wire, optionally with an intermediate annealing treatment for initial strengthening of the tube material.
The methods according to the prior art have the disadvantage in common that at least in part the filler flux is heated to high temperatures at which decomposition and/or oxidation reactions of the flux constituents can occur.
Another disadvantage can be given in that during the welding process, before welding on the electrode, the metallic surface thereof is oxidized and oxygen is thus incorporated into the molten metal of the weld seam.